Caucasians who have had a good deal of sun exposure in childhood will show the following gross cutaneous alterations in adult life: wrinkling, leatheriness, yellowing, looseness, roughness, dryness, mottling (hyperpigmentation) and various premalignant growths (often subclinical). These changes are most prominent in light-skinned persons who burn easily and tan poorly. The baleful effects of sunlight are cumulative, increasing with time. Although the anatomic degradation of the skin is most advanced in the elderly, the destructive effects of excessive sun exposure are already evident by the second decade. Serious microscopic alterations of the epidermis and dermis occur decades before these become clinically visible. Wrinkling, yellowing, leatheriness, loss of elasticity are very late changes.
It is known to use vitamin A acid for the treatment of acne as set forth in my U.S. Pat. No. 3,729,568. Other known uses of vitamin A acid which were reviewed by Thomas and Doyle in Journal of American Academy of Dermatology (May, 1981) Volume 4, No. 5, subsequent to completion of the present invention, include, in addition to acne treatment, treatment of senile comedones, nevus comedonicus, linear verrucous nevus, plantar warts, pseudofolliculitis, keratoacanthoma, solar keratosis of extremities, callosities, keratosis palmaris et plantaris, Darier's disease, ichthyosis, psoriasis, acanthosis nigricans, lichen planus, molluscum contagiosum, reactive perforating collagenosis, melasma, corneal epithelial peeling, geographic tongue, Fox-Fordyce disease, cutaneous metastatic melanoma and keloids or hypertrophic scars. Vitamin A acid derivatives (retinoids) are known to have prophylactic and therapeutic effects on a great variety of tumors and are being increasingly used as anti-tumor drugs.
In view of the foregoing, it is believed that vitamin A acid influences ultrastructural and proliferative properties of epidermal cells. However, these prior art uses of vitamin A acid have generally involved short term treatments in which relatively large doses of the acid are applied (i.e. sufficient to cause significant irritation and often peeling) in order to obtain a quick cure or treatment of the particular condition, such as removal of comedones, as opposed to persistent treatment of normal aging skin.